The present invention relates to an integral packing/covering member for a hard-disc unit or, more particularly, to such a member for a hard-disc unit formed by utilizing a self-adhesive liquid silicone rubber-based composition as a packing material in assemblage of the hard-disc unit.
The hard-disc unit here intended is a device comprising a discformed magnetic recording medium prepared by providing a disc of an aluminum alloy and the like with a magnetic recording layer, formed thereon by coating or sputtering, and having a casing containing the disc in a rotatable fashion so as to magnetically write information into the magnetic recording layer or read out the recorded information by means of a magnetic head held above the disc rotating at a high velocity with a very narrow gap of about 0.1 to 0.5 .mu.m therebetween. Among various requirements for such a device, it is very important to prevent trouble caused by the dust coming from outside of or produced inside of the device such trouble includes head crashes and damages to the magnetic recording layer.
Accordingly, it is conventional in hard-disc units in order to solve the above mentioned problems due to dust that dust-free air through a high-performance filter is circulated inside the casing under a controlled pressure and any gaps between the casing and various covers are sealed by providing packing of a rubbery material. Various synthetic rubbers are used for this purpose including polychloroprene rubbers, urethane rubbers, silicone rubbers, acrylonitrile-butadiene copolymeric rubbers and the like. These rubbers are shaped into the form of packing either by compression molding in a metal mold or by punching of a pre-shaped rubber sheet using a punching die. The packing can be prepared also from a sheet of foamed bodies of these rubbers or polyethylenes.
The use of the above mentioned packing shaped in advance by compression molding or punching is not always quite advantageous because the pre-shaped packing must be coated with a pressure-sensitive adhesive, and the adhesive-coated surface must be protected temporarily with a sheet of release paper. This requires substantial labor, in addition to that required since the packing must be mounted on the device with extremely high exactness to achieve the desired position this necessitates utmost skillfulness and great time consumption, unavoidably resulting in an increase in production costs. In addition, the fastening force required for obtaining reliable sealing is sometimes quite large so as to cause distortion of the covering member.
Needless to say, the packing used for the above mentioned application must be very clean so as not to cause dust formation or contamination. It is a rather difficult matter to completely prevent contamination from the curable or pressure-sensitive adhesives used thereon and, when the finishing work of a compression-molded packing is imperfect, burrs or fins remaining on the surface of the packing sometimes fall off to form dust particles. When the packing is prepared from a sheet of foamed rubber body, dust particles are sometimes enclosed in the cells of the cellular foamed body and, eventually, will come out.
Alternatively, a proposal has been made that, in place of using a pre-shaped rubber packing, a liquid rubber composition curable into rubber is spread over the covering member or the interstices between the casing and the covering are filled therewith followed by in situ curing into rubber. This method is indeed effective in preventing the adverse influences caused by dust particles entering from outside or occuring inside the. However, certain in situ curable rubber compositions exhibit the phenomenon of bleeding of an oily matter or blooming of a powdery matter on the surface of the cured rubber accordingly, no complete solution could be obtained for the problems due to contaminants or dust particles. It is known that in situ curable silicone rubber compositions are the most advantageous among various types of in situ curable rubber compositions, by virtue of their small amount of bleeding or blooming, but they are not free from the problem. This is due to the volatility of low molecular-weight organopolysiloxanes contained in the composition, which are vaporized inside the device and then deposited, causing troubles.
The inventors have previously proposed that the above mentioned problem due to the low molecular-weight organopolysiloxanes contained in the in situ curable silicone rubber composition can be solved by using a specific composition. By this means, the problems due to contaminants or dusts can be solved almost completely. Hard-disc units prepared by using such an in situ curable silicone rubber composition as the packing material, however, are not without other problems. One of the problems still to be solved is relative to the transmission of vibration depending on the vibration-damping characteristic and sound-absorbing characteristic of the cured rubber, sometimes adversely influencing on the performance of the device.